Electric furnace



Dec. 3, 1929.

A. N. OTIS ET, AL

ELECTRIC FURNACE Filed Oct. 24. 1928 Inventor: Albert N. O-tis, 42%; Hege" DH 564 Their Attorney.

Patented Dec. 3, 1929 UNITED STATES PATENT OFFICE ALBERT N. OTIS AND GEORGE W. HEGEL, F SCHENECTADY, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION NEW YORK ELECTRIC FURNACE Application filed October .24, 1928. Serial No. 314,752.

7 the furnace chamber.

In carrying out our invention in one form, we support a resistor on a plurality of refractory supporting members arranged horizontally in the upper part of the heating chamber and supported at one end directly by the furnace wall and at the other end by a transverse beam, this beam extending across the front of the heating chamber and being secured at its ends to the furnace side walls. We also provide the front furnace wall with a removable portion so that, by

removing this portion, the resistor may beremoved from or placed upon the supporting members from in front of the furnace. The transverse beam .and supporting members are so arranged that when the resistor is in position these members and the transverse beam are secured in position. The danger of twisting or breaking the resistor in case the su porting framework should be accidental ly removed, is thus obviated. Our invention also contemplates the use of novel spacing means whereby the convolutions of a resistor are maintained in proper spaced relation.

I For a better understanding of our invention, reference may be had to the accompanying drawing in which Flg. 1 is an elevat on mostly in section of a furnace embody ng our invention; Fig. 2 is a front elevation partly in section of the furnace shown in Fig. 1; Fig. 3 is a perspective view of the transverse beam and one end of the tubular members and heatlng resistor; Fig. 4 is an enlarged View of a portion of the inner wall of the furnace, while Fig. 5 is a perspective view'of a spacing block.

Referring to theidrawing, in carrying out our invention in one form, we provide a furnace structure comprising an outer metal casing and an inner lining or wall 11 of heat refractory material defining a heating chamber 12. The spacebetween the inner lining or wall 11 and the outer metal casing 10 is preferably filled with some suitable n heating insulating material 13 such as rockwool or diatomaceous earth. Theinner refractory wall 11 is supported upon a plurality of blocks 14 of heat insulating material. The front wall of the outer casing 10 is provided with a removable portion 15, this removable portion being secured to the front wall by means of suitable bolts 16. A vertically movable heat insulated door 17 is slldably mounted on the removable wall portion 15, this door being suspended by a cable 18 attached to one end of a counter-weighted arm 19 pivotally secured to the removable wall portion 15. A handle 20 is secured to the outer end of the pivoted arm 19, and by pulling this handle downwardly the door 17 will be elevated thus giving access to the front of the heating chamber 12. The door 17 is provided with a sight opening 21 covered by a small pivoted door 22. A block 23' of heat refractory insulating material, the purpose of which will be hereinafter explained, is removably supported in' the up per part of the front end of the heating chamber 12.

In accordance with our invention, we have provided a framework for horizontally supporting an electric heating resistor 25 in the upper part of the heating chamber 12. This framework comprises a cast metal beam 26, made of a suitable heat resisting alloy such as an alloy of nickel, chro' mium and iron, and a pair of tubular heat refractory insulating members or bars 27. The beam 26 is provided atits ends with offset portions having downwardly extending tabs 28, and with a pair of lateral projec tions 29 extending from one side. These projections 29 are slightly smaller than the holes in the tubular members 27 and when the framework is in position the forward ends of the tubular members 27 incase the projections 29. The beam 26 is adapted to be placed horizontally across the upper forward part of the heating chamber 12, the tabs 28 engaging recesses 30 in the side walls-of the inner lining 11. The rear wall. of the inner lining 11 is provided with a pair of recesses 31 adapted to receive the rearward ends of the tubular members 27, as shown more clearly in Fig. 1. v

The heating resistor 25 is formed of a suitable heat resistant metal, preferably an alloy of nickel and chromium, and is bent into a plurality of flattened loops or convolutions, the length of these convolutions being greater than the distance between the tubular members 27. The resistor 25 is provided at its ends with terminal strips 32, these strips being bent so as to pass through apertures in the furnace walls. In order to maintain the convolutions of the resistor 25 in proper spaced relation, thereby preventing short circuiting of portions of the resistor and damage resulting therefrom, we have provided spacing means comprising a plurality of rectangular blocks 33 of refractory insulating material such as aluminum oxide, each block having a plurality of depending projections 34, substantially oval or circular in cross-section. One of the blocks 33 is shown more clearly in Fig. 5. The roof of the inner wall or lining 11 is provided with grooves or recesses 35 and 36 extendin longitudinally of the heating chamber 12, t ese grooves being slightly wider than the blocks 33.

In placing the resistor 25 in the heating chamber 12 the portion 15 of the outer front walls is removed as well as the refractory block 23. The tubular members 27 are then placed in the heating chamber, their rearward ends resting in the recesses 31 inv the rear wall. The projections 29 of the beam 26 are placed in the holes in the forward ends of the tubular members 27 and the tabs 28 at the ends of the beam are then placed in the recesses 30 in the side walls of-the inner lining '11. The refractory spacing blocks 33 are placed in end to end re ation along the resistor 25 with the projections 34 extending downwardly between the parallel lengths of refractory block 23 and the removable the resistor, as is shown in Fig. 1. The resistor 25 may then be slid into place over the tubular members 27, care being taken that the terminals 32 pass through the apertures provided for them in the-furnace walls and that the spacing blocks 33 pass within the grooves in the roof of the inner wall 11. The

ortion 15 of the front wall are then retui ned and secured into osition. It will be observed that since t e tabs 28 at the ends of the beam 26 extend downwardly into the rece'sses 30, the tubes 27 and beam- 26 cannot be removed without moving the beam 26 upwardl and outwardly or to the left in viewing ig. 1. Due to the presence of the resistor 25 and spacing blocks 33 directl above the tubes 27, and the refractory blocii 23 directly in front of thebeam'26, such a movement of the framework is impossible.

. We have also provided a heating resistor'37 in the bottom part of the heating chamber 12.

The resistor 37 is formed into a plurality of flattened oonvolutions and is supported by refractory spacing members .38 running lengthwise of the heating chamber and resting on the bottom wall thereof. A heat refractory metal hearth plate or pan 39 is supported over the resistor 37 on blocks 40 of heat insulating material provided for this purpose. The resistor 37 is also provided with terminal strips, these terminal strips passing through apertures in the bottom and rear walls of the furnace. We have shown the terminal strips of the heating resistors 25 and 37 as passing through the rear wall of the furnace, connections being made to the terminals so that the resistors are connected in series. Suitable control devices, not shown, such as a thermocouple and a temperature limit fuse may be inserted in the wall of the furnace, openings 41 and 42 being provided for this rupose. A'metal terminal box 43 is attac led to the rear wall of the furnace to house the control devices and the terminals withtheir connections. While we have shown the resistors 25 and 37 as being connected electrically in series, it is to be understood that other suitable connections may be used. For, instance, either one of the resistors may be used alone or the resistors may be'connected in parallel, and through suitable switching means any one of these arrangements may be used de ending on the temperature desired in the eating chamber 12.

While we have shown but one transverse supporting beam 26, it is to be understood that more than one of these beams may be used. In the case of a furnace having an elongated heating chamber, several sets of tubular members 27 may be used, the adjacent ends of these members being supported by beams similar to beam 26, arranged intermediate the front and rear walls of the furnace and sup orted by the side walls thereof.

From the oregoing description it' will be observed that we have provided a rigidly supported framework over which the heating resistors may be readily placed into or removed A from the furnace. The upper framework is so supported that when the resistor 25 is in position the framework cannot be removed, and the danger of bending or breaking the resistor due to moving the supporting frame is thus obviated. Due to the tubular shape of the supports 27, line contact is formed between the tubular members and the resistor 25 and localization of heat at the points of su port is thus decreased to a minimum. he spacing blocks 33 are prevented by the grooves 35 and 36 from being displaced and the projections 34 onfthe spacing blocks maintain the parallel lengths of the resistor 25 in proper spaced relation.

While we have described our invention as embodied in concreteform and operating I 'is set forth in the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric furnace, heat insulating top, bottom and side walls defining a heating chamber, a removable heat refractory framework supported by said side walls, and an electric heating resistor removably mounted on said frame work so as to secure said framework in position.

2. In a furnace, heat insulatin walls defining a heating chamber, a mem er removably supported b said walls and extending across said chamber, a lurality of heat refractory bars supported y said member, and an electric heating resistor mounted upon said bars so as to secure said member in position.

3. In a furnace; heat insulating walls defining a heating chamber, a member supported by said walls and extending across one end of said chamber, a plurality of heat refractory bars supported by said walls and said member, and an electric heating resistor mounted on said bars so as to secure them in position.

4. In a furnace, heat insulated walls defining a heating chamber, a member supported by said walls transversely in said chamber, heat refractory bars extending longitudinally in said chamber, said bars being supported at one end by said transverse member, a sinuous electric heating resistor mounted upon said bars, and means cooperating with the roof of said heating chamber for maintainin the convolutions of said resistor in space relation.

5. In a furnace, heat insulated walls therefor, an inner lining of heat refractory material defining a heating chamber, a beam supported by said lining, a plurality of bars of heat refractory material supported at one end by said beam, and an electric heating resistor mounted upon said bars.

6. In a furnace, heat insulated outer walls therefor, inner heat refractory walls defining a heating chamber, said inner walls being provided with recesses at the rear of said chamber, a beam supported by said inner walls and extending transversely across the forward end of said chamber, a plurality of refractory bars supported at one end in said recesses and at the other end by said beam, sinuous electric heating resistor mounted upon said bars, and means formaintai the con.- volutions of said resistor in. space relation to each other.

7. In an electric furnace, heat insulating walls defining a heating chamber, said walls having, a removable front ortion, a transverse bea'm supported by sai walls across the forward end of said chamber, a plurality of elongated,'heat refractory members extending substantially horizontally from front to back of said chamber, said members being supported at the front end by said beam, and an electric heating resistor supported upon said elongated members.

8. In an electric furnace, heat insulated walls defining a heating chamber, a heat refractory member supported by said walls and extending across the. forward end of said chamber, a plurality of heat refractory tubes extending substantially horizontally across said chamber, said tubes being supported at one end by said member, and a sinuous electric heating resistor mounted upon said tubes.

9. An electric furnace comprising heat in sulated walls defining a heating chamber, a beam supported by the side walls and extending across the upper forward portion of said chamber, a plurality of horizontally arranged heat refractory tubes supported at one end by said beam, a convoluted ribbon resistor mounted upon said tubes in close proximity to the roof of said chamber, a plurality of refractory spacing blocks, projections on said blocks extending between adjacent convolutions of said resistor, and means for preventing sidewise movement of said blocks.

10. An electric furnace, comprising heat insulated outer walls, a heat refractory inner wall defining a heating chamber, said outer walls having a removable front ortion, a beam supported by said inner wa l and extending transversely across said chamber directly at the rear of said removable wall portion, a plurality of tubular heat' refractory members supported by said beam, and

a sinuous ribbon resistor slidably mounted on said tubular members so as to be re'movable through the front portion of said outer walls.

11. An electric furnace, comprising heat insulated walls defining a heating chamber, the roof of said chamber being provided with longitudinal grooves, a metallic beam supported at its ends by said walls and extending across the upper, forward end of said chamber, lateral projections on said beam, a plurality of heat refractory tubular members extending from front to back across said chamber, the forward end of said tubular members incasing said projections and the rearward ends of said tubular members being supported by the rear wall of said chamber, an electric resistor comprising a plurality of flattened loops supported on said tubular members, said loops being arranged substantially at right angles to said tubular members, a plurality of refractory spacing blocks slidably mounted in said longitudinal grooves,

4 1,7'ss,44e

and projections on said blocks extending downwardly between adjacent loops of said resistor for maintaining said loops in spaced relation to each other.

In Witness whereof, We have hereunto set 5 our hands this 23rd day of October, 1928.

ALBERT N. OTIS. GEORGE W. HEGEL. 

